i noticed that when the "smart volume" setting is off, i can hear a low hum from the unit(only when music is playing, but i can still hear it when the volume is at zero), and when i turn it on, it goes away completely. just wondering if anyone else has the same thing going on? is it normal to hear low hum while smart volume is turned off? also, i believe this isn't true but i heard someone say smart volume eats battery? could that be true by any chance?